The surface linings of walls and ceiling are crucial for the early develoment of a room fire

Flash over occurs at a temperature of about 600°C

The maximum air temperature for safe evacuation is appr. 80°C

Requirements on suspended ceilings

The fire safety demands on suspended ceilings can vary depending on both the type of room and building where they are to be installed. Detailed requirements can be found in the national building regulations. Two general requirements can, however, be identified as crucial for suspended ceilings in the early stages of fire, and they should be regarded as "compulsory" in all premises.

They must only make a negligible contribution to the fire development and to the production of smoke. This is fulfilled by using a ceiling consisting of materials and surface linings complying with at least Euroclass B-s1, d0.

They must not break and collapse during the early stages of the fire when evacuation and rescue operations can still be carried out. To pass this requirement a ceiling system should be able to withstand a heat exposure of approx. 300°C. (The heat radiation from a smoke gas layer with a temperature of 300°C corresponds approximately to what a fully equipped fire fighter can withstand.)

Fire safety in buildings

The main purpose of the fire safety design of a building is to minimise the consequences of a fire. Principally, it concerns the prevention of injury to people but it also entails limiting the material and economic damage which is likely to ensue.

In a burning building the circumstances can quickly become such that there is imminent risk of personal injury. Within the parameters of safe evacuation, consideration must be given to fire gases, visibility, heat radiation and temperature. E.g. in order to evacuate safely, the air temperature in rooms through which people are escaping should not exceed approx. 80°C.

The total fire protection of a building and its specific function is a complex issue, comprising several areas and how they interact with one another:

The building itself including its design, building elements, materials, interior fittings and furnishing

The fire detection systems and alarms

The organisation and practice of conducting evacuation, e.g. in schools and nursing homes

The rescue efforts of fire brigades

The extinguishing and control of the fire. Partly through automatic fire extinguishing systems and/or partly through active actions, e.g. of the fire brigade

Building regulations and various types of standards normally cover these aspects. The building regulations are formulated on a national basis and vary between different countries. Standards can be on either a national base (e.g. DIN, BS and ASTM) or international (EN- and ISO-standards).

A room fire can be divided into various phases. The incipient phase or beginning of a fire is dependent on the size of the ignition source and the properties of the materials and objects that are directly affected. During the growth phase the fire increases in size and other objects around the fire origin will begin to burn. Even the surface linings of the walls, floor and ceiling close to the fire can ignite. Increasing amounts of smoke and heat begin to develop and a layer of hot fire gases forms beneath the ceiling.

In the growth phase the fire is local. The fire characteristics of the surface linings play an important part in the fire development.

During the growth phase flashover can occur. This is when the intensity of the fire is so great that it ceases to remain local but involves all combustible material in the room. A large amount of heat is released and flames burst out through windows and door openings. Generally, flashover occurs once the fire gases in the room reach 500-600°C. The heat radiation from the layer of fire gases is so great at this stage that it causes all combustible materials to ignite. Flashover can occur just a few minutes after ignition. However, it can also be delayed or avoided altogether. This could be the case in a room which has just a small amount of combustible furnishings and is equipped with surface linings that make just a negligible contribution to the fire development. After flashover the fire reaches its maximum level and is fully developed. The length and intensity of the fire is now mainly determined by the supply of air and the fire load, i.e. the amount of combustible materials present.

The decay phase is when the fire fades out.

At the point of flashover the entire room is engulfed by the fire and large flames burst out from door and window openings. The fire can now spread to other parts of the building.

Testing and classification of products

Fire testing methods are generally designed to simulate the different phases of the fire process. Consequently, tests on surface linings are conducted using fire sources representative of the incipient and growth phases of a fire. These test methods are referred to as "reaction to fire" tests and the purpose is to evalutate the contribution of products and materials to the early stages of a fire in terms of:

Ignitability

Flame spread

Heat release

Smoke production

Occurrence of flaming droplets/particles

Normally reaction to fire tests are carried out in small or intermediate scale. Complete building elements (doors, floor structures, partitions etc.) which are used for separating fire compartments are tested for the case of a fully developed fire. These test methods are called "fire resistance" and are carried out in full scale. The temperature in the test furnace follows the so-called "standard fire curve" which is designed to represent a fully developed fire. The properties that are evaluated are:

Insulation (ability to reduce the heat transfer)

Integrity (ability to prevent leakage of flames and hot gases)

Load bearing capacity

Building elements classified as "fire resistant" with respect to integrity and insulation are used as a means to prevent fire being spread between fire compartments.

The European system

The reaction to fire testing and classification system for linings and materials in Europe is called Euroclass. Altogether there are 39 classes divided into 7 main levels; A1, A2, B, C, D, E and F where A1 is the best and F are for products and materials not classified.

Most of the main classes also include an additional classification regarding smoke production and the occurrence of flaming droplets/particles. The classes for smoke are s1, s2 and s3, where s1 is the best. The classes for flaming droplets and particles are d0, d1 and d2, where d0 is the best.

1 = Main class

2= Smoke production

3 = Occurence of flaming droplets/particles

Euroclasses fire table

Euroclasses

A1

A2-s1,d0

A2-s1,d1

A2-s1,d2

A2-s2,d0

A2-s2,d1

A2-s2,d2

A2-s3,d0

A2-s3,d1

A2-s3,d2

B-s1,d0

B-s1,d1

B-s1,d2

B-s2,d0

B-s2,d1

B-s2,d2

B-s3,d0

B-s3,d1

B-s3,d2

C-s1,d0

C-s1,d1

C-s1,d2

C-s2,d0

C-s2,d1

C-s2,d2

C-s3,d0

C-s3,d1

C-s3,d2

D-s1,d0

D-s1,d1

D-s1,d2

D-s2,d0

D-s2,d1

D-s2,d2

D-s3,d0

D-s3,d1

D-s3,d2

E

E-d2

F

Euroclasses according to classification standard EN 13501-1 Fire classification of construction products and building elements - Part 1 Classification using test data from reaction to fire tests.

1. Temperature

2. Flash over

3. Incipient

4. Growth

5. Fully developed

6. Decay

7. Time

8. Euroclasses

9. Fire resistance classes

The graph shows the relationship between fire process and the fire classes

Fire resistance

The main classes used for the fire resistance classification of building elements are:

R = Load bearing capacity

E = Integrity (ability to prevent leakage of flames and hot gases)

I = Insulation (ability to reduce the heat transfer)

The classes are always combined with a time class expressed in minutes. These time classes could be from 15 up to 360 minutes in steps defined in the classification standard EN 13501-2. A separating and load bearing wall could for example be classified as REI 60, which means that it will retain its load bearing capacity as well as its fire separating function during 60 minutes of a fully developed fire.

A non-load bearing element will only be given the classification EI or E combined with a time class. The latter case is for example relevant for special fire glazed partitions which will prevent the penetration of flames and hot gases but not provide insulation against heat. A load bearing column, which is obviously not a separating element, can, accordingly, only have the fire resistance class R combined with a time class.

1 = Load bearing capacity

2 = Integrity (ability to prevent leakage of flames and hot gases)

3 = Insulation (ability to reduce the heat transfer)

4 = Time class in minutes

The ASTM system

Reaction to fire

In the US market products are tested and classified according to ASTM standards (American Society for Testing and Materials).

Flame spread and smoke production of surface linings, for example on ceilings, are tested and evaluated according to ASTM E 84 "Surface Burning Characteristics of Building Materials". A smoke production index and flame spread index is then derived from the measurements that are taken.

(The test apparatus consists of a 25 feet (7.6 m) long horizontal "tunnel furnace" with a cross sectional area of approximately 12'1/2 x 17'3/4 in (305 x 450 mm).The interior surfaces are covered with the test material and a burner is applied at one end of the tunnel. In the other end there is a fan creating a draft forcing the flames to propagate into the tunnel. The test lasts ten minutes.)

Acoustic ceiling products are classified according to ASTM E 1264. Three fire classes are defined; A, B and C. The classes are equivalent to classes I, II and III, respectively, of various building code authorities. Class A (I) is the best.

Reaction to fire

ASTM fire classes. In addition, for class A ceiling products the material should not show evidence of continuos progressive combustion after the test flame has been extinguished.

Max allowed index

class

Flame spread

Smoke development

A

25

50

B

75

-

C

200

-

Fire resistance

Fire separating elements, such as fire walls and floor structures, are tested and evaluated in accordance with ASTM E 119 "Fire Tests of Building Construction and Materials". The tests are carried out in full scale. The test specimens are subjected to a heat exposure that corresponds to a fully developed fire.